The present invention relates to carbon nanotube composite materials and, more particularly, to a blended composite polymeric material with both un-functionalized and hydroxylated carbon nanotubes.
Carbon nanotube (CNT) filled polymer nanocomposites are promising materials for a variety of applications, with enhanced mechanical, thermal and electronic properties imparted to the polymer matrix by mixing even minute amounts (<0.1 wt %) of CNTs. These polymer composite materials containing carbon-based fillers (carbon nanotubes) can be useful because of their potential for high conductivity, low weight and ease of processing. Of particular interest is the formation of CNT networks in a polymer film to create electrically conductive pathways. Useful would be an efficient method for imparting the high electrical conductivity of individual CNTs to a composite material. For a network of CNTs to form an electrically conductive path requires a minimum overlap of tubes, which is otherwise known as the percolation threshold. Van der Waals interactions between CNTs leads to aggregation and bundling into large clusters, which is a fundamental challenge to achieving maximum dispersion and conductivity for a given amount of CNTs. To compensate for this aggregation and achieve a conductive pathway through a filled polymer matrix, the fraction of CNTs is generally increased beyond the minimum fill required for a theoretical percolation network. One method to increase the dispersion of CNTs in various matrix materials is through pre-treatment functionalization methods and mixing procedures to obtain enhanced properties at lower fill percentages. Generally, the increased dispersion from functionalization of CNT outer walls comes at the expense of carbon-carbon bond cleavage and reduction in the π-bonding network, which leads to a loss of electrical conductivity. Another CNT dispersion enhancement strategy is to utilize small molecule and oligomeric additives that have high affinity for the CNT surface and can wrap around tubes to reduce aggregation via non-covalent functionalization. This strategy has proven highly useful at maintaining the desired charge transport properties of CNTs while enhancing dispersion to form percolated networks at lower fill percentages.